BULLETIN 


5* 

OF  THE 

SOUTH  DAKOTA  SCHOOL  OF  MINES. 


NOTES  ON  THE 

GEOLOGY  AND  MINERAL  DEPOSITS 

OF  A PORTION  OF  THE 

SOUTHERN  BLACK  HILLS. 


Rapid  City,  South  Dakota. 
January,  1899. 


A 


) 


GENERAL  GEOLOGY. 


BY  CLEOPHAS  C.  O’HARRA. 


Introductory. 

It  is  the  established  custom  of  the  State  School  of 
Mines  to  provide  means  for  the  field  study  of  various 
geological,  mineralogdcal  and  mining  problems  relating 
to  the  state.  In  accordance  with  this  custom,  a few 
weeks  were  spent  by  the  school  survey  party  in  the 
Southern  Black  Hills  during  the  past  summer.  The 
party  for  a portion  of  the  time  numbered  six,  includ- 
ing professors  and  students."  In  so  far  as  convenient, 
the  work  was  carried  on  with  the  view  of  training  the 
students  of  the  party  in  the  methods  best  adapted  to 
the  study  of  field  geology.  Every  effort,  however,  was 
put  forth  in  order  that  new  facts  might  be  gained 
which  would  aid  in  unravelling  the  geological  history 
and  the  economic  possibilities  of  the  region. 

It  was  with  this  latter  idea  definitely  in  view  that  our 
party  selected  for  examination  that  portion  of  the  pre- 
Cambrian  rocks  of  the  Southern  Hills,  which  lies  in 
the  north  central  part  of  Custer  County,  southeast  of 
Harney  peak.  More  definitely,  the  particular  area  to 
which  most  of  our  attention  was  directed,  may  be  de- 
scribed as  bounded  on  the  north  by  a line  correspond- 
ing approximately  with  latitude  43°  50  r,  which  crosses 

*The  author  of  this  paper  wishes  to  make  particular  acknowledgment  to 
Professor  McLaury  for  assistance  rendered  in  connection  with  the  field  work. 

/9  Vr 


4 BULLETIN  OF  THE  SOUTH  DAKOTA  SCHOOL  OF  MINES. 


the  head-waters  of  Iron  creek  and  Spokane  creek 
(sometimes  known  as  Little  Squaw  creek),  on  the 
east  by  the  Cambrian  quartzite,  * on  the  south  by 
French  creek,  and  on  the  west  by  the  meridian  of 
103°  30'  west  longitude.  The  survey  camp  was  situ- 
ated in  the  west  central  part  of  the  area  seven  miles 
N.  80°  E.  of  Custer,  and  eig'ht  and  one-half  miles  S. 
12°  W.  of  Keystone.  In  addition  to  the  study  in  this 
area,  several  neighboring  localities  of  especial  interest 
were  also  visited. 

The  position  of  the  area,  with  reference  to  the  gen- 
eral Black  Hills  region,  may  be  seen  in  the  accompany- 

It  is  well  known  that 
of  the  large  amount  of 
valuable  mineral  pro- 
ducts now  obtained  in 
the  Black  Hills,  by  far 
the  larger  part  comes 
from  the  Northern 
Hills.  This  is  particu- 
larly true  of  gold.  The 
Southern  Hills  have 
hitherto  produced  only 
a comparatively  small 
amount.  However,  dili- 
gent prospecting  has 
revealed  the  fact  that 
rich  gold  ore  exists 
there  in  areas  of  considerable  extent-  and  in  one  or 
more  places,  extremely  handsome  returns  are  now 
being  realized.  Little  or  no  detailed  scientific  work 
has  hitherto  been  carried  on  for  the  purpose  of  solv- 
ing* the  economic  problems  of  the  gold-bearing  rocks 
in  the  restricted  area  to  be  discussed  in  this  paper. 
Our  party  has  endeavored  to  supply,  as  best  it  could, 
the  want  in  this  direction. 


ing  sketch  map,  figure  1. 


*This  is  the  so-called  Potsdam  of  the  Black  Hills.  During  the  time  at 
our  disposal  only  the  general  position  of  this  contact  line  could  be  mapped. 


BULLETIN  OF  TIIE  SOUTH  DAKOTA  SCHOOL  OF  MINES.  5 


Topography. 

:ally  the  region  is  sharply  separated  into 
two  divisions^  A rather  prominent  but  somewhat 


irregular  line  of  ridges  beginning  a short  distance  west 
of  Spokane  and  running  in  a general  southwesterly 
direction  marks  the  line  of  separation,  (see  the  geologi- 
cal map,  figure  4).  The  area  to  the  west  is  occupied 
by  granites,  schists,  and  quartzites,  the  granite  greatly 
predominating.  East  of  the  line  of  separation  and  in- 
cluding the  line  of  ridges  mentioned,  the  rocks  are  also 
granites,  schists  and  quartzites,  but,  unlike  the  west- 
ern area,  the  prevailing  rocks  here  are  quartzites. 
This  diversity  in  rock  character  is  the  chief  cause  of 
the  marked  difference  in  topographic  features. 

<£he  western  topographic  area  is,  in  general,  ex- 
tremely rough  and  difficult  to  traverse.  The  granite 
is  exposed  in  numerous  mountain  peaks,  serrated 
ridges,  slender  pinnacles,  sharp  needles,  and  lenticular 
masses  projecting  frequently  to  considerable  heights 
above  the  general  surface.  rNewton,  in  the  Geology  of  the 
Black  Hills*  has  described  to  some  extent  the  general 
surface  features  of  the  granite  district  but  no  one  can 
fully  appreciate  his  graphic  description  of  the  delays 
and  hardships  encountered  by  his  party  in  their 
attempt  to  reach  Harney  peak  until  he  himself  has 
tried  to  follow  a direct  course  for  several  miles  over 
this  extremely  rough  granite  surface]  Here  and  there 
a small  park  is  found  which,  when  cleared  of  forest  and 
properly  irrigated,  furnishes  a fruitful  field  and  a 
comfortable  home  for  the  careful  ranchman.  The 
numerous  little  angular  valleys  and  small  parks,  as  well 
as  the  high  rounded  shoulders  of  the  larger  peaks  are 
generally  covered  by  a considerable  growth  of  pine 
trees,  which  conceal  from  the  distant  observer  all  but 
the  clean  precipitous  sides  of  the  higher  granite 
masses,  and  thus  add  a pleasant  charm  to  this  most 


beautiful  mountain  scenery. 


0 


* Report  on  the  Geology  and  Resources  of  the  Black  Hills  of  Dakota,  with 
atlas.  By  Henry  Newton,  E.  M.,  and  Walter  P.  Jenney,  E.  M.,  Washington, 
1880. 


6 BULLETIN  OF  THE  SOUTH  DAKOT^  SCHOOL  OF  MINES. 


LPig-ure  2 shows  the  granite  area  as  seen  from  the 
top  of  Saddleback  ridg-e  looking-  toward  Harney  peak. 

The  surface  of  the  eastern  topographic  area,  althoug-h 
in  many  places  quite  rougfh  and  showing-  narrow  ravines, 
deep  g-ulches  and  precipitous  canyons,  has  little  or 
none  of  that  roug-h  jag-g-ed  appearance  of  the  granite 
area.  Here  the  surface  is  undulating-  and  the  hillsides 
are  g-enerally  covered  by  a heavy  soil  and  a dense 
timber  growth  to  the  very  top.  Sharply  rounded  hills 
and  narrow-crested,  irregrdarly  curving-  ridg-es  separ 
ated  by  deep  winding-  valleys  are  the  rule.  Fig-ure  3 
shows  the  surface  features  of  this  region  as  seen  from 
near  the  top  of  Chilkoot  hill,  looking-  southward  toward 
Sheep  mountain. 

Drainage. 

Battle  creek  and  French  creek  drain  the  area,  their 
waters  flowing-  eastward  into  the  prairie  region  and 
finally  emptying-  into  the  south  fork  of  the  Cheyenne 
river.  Of  these,  French  creek,  which  in  this  part  of 
the  Hills  is  considerably  the  strong-er  of  the  two 
streams,  drains  only  a small  portion  of  the  area,  the 
divide  being-  situated  within  two  or  three  miles  of  the 
creek.  Several  small  branches  carry  the  water  from  the 
remainder  of  the  area  in  a g-eneral  northeasterly  direc- 
tion to  Battle  creek.  Among-  these  smaller  streams 
are  Iron  creek,  which  joins  Battle  creek  near  Hayward 
and  Squaw  creek  which  flows  into  Battle  creek  two 
miles  southwest  of  Hermosa.  Squaw  creek  itself  re- 
ceives water  from  several  smaller  streams  of  some 
importance,  the  local  names  for  which  are  Spokane 
creek  (Little  Squaw  creek),  Bear  g-ulch,  Middle  Squaw 
creek  and  South  Squaw  creek.  Some  of  these  streams 
in  various  parts  of  their  courses  have  cut  deep  g-org-es 
or  canyons  and  throug-hout  the  ,upper  part  of  their 
courses  the  descent  is  rapid.  In  their  lower  courses 
the  current  is  less  swift  and  in  several  cases  the 
water  sinks  beneath  the  surface  and  disappears  so  that 
throug-hout  much  of  the  year  this  part  of  the  stream 
bed  is  dry.  Furthermore,  on  account  of  the  deficiency 
of  rainfall,  many  of  the  smaller  stream  beds,  in  the 


) 


BULLETIN  OF  THE  SOUTH  DAKOTA  SCHOOL  OF  MINES, 


i 


Figure  2.  Granite  area  as  seen  from  Saddleback  ridge.  Harney  Peak  in  the  distance. 


BULLETIN  OF  THE  SOUTH  DAKOTA  SCHOOL  OF  MINKS 


t 


Figure  3.  Quartzite  area  as  seen  from  near  the  top  of  Chilkoot  hill.  Siieep  mountain  in  the  distance. 


BULLETIN  OF  THE  SOUTH  DAKOTA  SCHOOL  OF  MINES.  H 


more  elevated  portions  of  the  area,  are  wholly  dry 
throughout  much  of  the  year. 

Altitude. 

The  highest  point  in  the  area  is  Sheep  mountain,  near 
French  creek,  which  reaches  a height  of  6050  feet  above 
sea  level. * North  of  this  point  the  height  over  a 
considerable  portion  of  the  area  is  more  than  5500 
feet,  and  in  the  northwestern  part  one  or  two  isolated 
granite  peaks  closely  rival  Sheep  mountain  in  height. 
The  lowest  point  is  about  4000  feet,  which  altitude  is 
reached  along  some  of  the  creek  beds  near  the  eastern 
border  of  the  area.  For  the  whole  area,  the  average 
elevation  is  perhaps  not  far  from  5300  feet. 

Geology. 

As  previously  stated,  the  rocks  of  the  area  are  gran- 
ites, quartzites  and  schists  (see  figure  4).  Granites 


Figure  4.  Geological  map.  Topography  reduced  from 
M Hermosa  sheet,  U.  S.  G.  S.,  1894. 


* Hermosa  sheet,  U.  S.  G.  S.,  1894. 


12  BULLETIN  OF  THE  SOUTH  DAKOTA  SCHOOL  OF  MINES. 


prevail  in  the  western  part,  quartzites  in  the  eastern. 
Schists  are  common  to  both.)  In  this  paper,  we  shall 
include  all  of  these  rocks  under  the  name  Pre- 
Cambrian,  the  authority  for  this  being*  based  on  con- 
clusive evidence.  Newton,  in  discussing-  the  ag*e  of  the 
granite,  savs,  in  reference  to  the  section  along*  French 
creek,  “A  continuous  sheet  of  Potsdam  passes  from  a 
surface  of  eroded  schist  to  a surface  of  granite.  There 
was  found  no  intrusion  of  the  granite  along*  the  parting* 
between  the  Potsdam  and  the  schists  and  there  was 
found  no  metamorphism  of  the  Potsdam  at  the  surface 
of  contact  with  the  granite.*  Similar  phenomena  as 
well  as  additional  evidence  were  found  by  Professor 
Headden  in  the  vicinity  of  Hayward  on  Battle  creek. t 
In  several  places  examined  by  us  between  these  sec- 
tions, the  evidence  is  as  unmistakable.  £Pig*ure  5 gives  a 
view  of  the  Cambrian  quartzite,  as  shown  on  Squaw 
creek  at  the  north  side  of  the  county  road,  one  mile 
east  of  Otis.  Here  the  Cambrian  quartzite,  the  lowest 
part  of  which  is  frequently  coarsely  conglomerate,  lies 
directly  upon  a medium  coarse  granite.  Two  expos- 
ures of  the  granite  are  shown  in  the  plate,  the  larg*est 
one  disclosing*  the  contact  line  for  a distance  of  twenty 
feet  or  more.  The  overlying*  Cambrian  quartzite  is 
wholly  unchang*ed  so  far  as  affected  by  the  presence  of 
the  granite. 

Pi  g*ure  6 shows  a similar  contact  exposed  on  the  north 
bank  of  Dry  creek,  two  hundred  yards  north  of  the 
Custer-Fair  burn  road,  a little  more  than  a mile  south- 
southeast  of  Otis.  Here,  however,  the  underiving*  coarse 
granite  is  present  only  in  the  form  of  clearly  defined 
dikes  wrhich,  having*  broken  throug*h  the  pre-Cambrian 
quartzite,  extend  upward  to  the  Cambrian  quartzite, 
where  they  are  sharply  truncated  on  a level  with  the 
eroded  surface  of  the  pre-Cambrian,  which  is  uncon- 
formably  overlain  by  the  Cambrian  quartzite.  The 


* Geology  of  the  Black  Hills  of  Dakota,  p.  78. 

| Van  Hise,  C.  R.  The  Pre-Cambrian  Rock  of  the  Black  Hills,  Bull, 
G.  S.  A.,  Vol.  I,  p.  212,  Washington,  1890. 


BULLETIN  OF  THE  SOUTH  DAKOTA  SCHOOL  OF  MINES.  13 


* 


Figure  5.  Cambrian — Pke-Cambrian  Contact  near  Otis. 


BULLETIN  OF  THE  SOUTH  DAKOTA  SCHOOL  OF  MINES.  17 


* 


dikes  shown  in  the  plate  are  pegmatitic  in  character, 
and  are  four  in  number.  The  one  farthest  east  is  ten 
inches  thick,  the  next  two  inches,  the  third  fourteen 
inches,  and  the  fourth,  the  one  farthest  west,  beneath 
the  opening-,  is  six  feet. 

Granite . — The  g'ranite  is  much  the  same  in  general 
character  throughout  the  entire  area.  It  is  made  up 
of  white  or  pinkish  feldspar,  clear,  smoky  or  rose 
quartz,  and  light  or  dark  mica,  besides  numerous 
accessory  minerals.  Among  the  latter,  tourmaline  is 
particularly  abundant.  The  percentage  of  feldspar  is 
high.  According  to  Newton,  the  Black  Hills  granite 
as  a whole  is  made  up  of  about  70  or  75  per  cent  of  feld- 
spar, 20  per  cent  of  quartz  and  5 per  cent  of  mica.* 
The  texture  varies  within  rather  wide  limits  but  it  is 
in  general  very  coarse.  Medium  grained  granite  is  not 
uncommon  over  considerable  areas,  but  the  finer  varie- 
ties are  almost  wholly  lacking.  Much  of  the  rock  is 
made  up  of  very  large  crystals  and  frequently  in- 
stead of  the  several  minerals  being  uniformly  distrib- 
uted throughout  the  mass  each  one  is  arranged  in 
extremely  irregular  segregations.  This  prominent 
coarse  nature  of  the  crystals  together  with  other 
phenomena  has  given  rise  to  various  views  concerning 
the  origin  of  the  granite,  t We  shall  make  no 
attempt  in  the  present  paper  to  enter  into  the  dis- 
cussion of  this  question. 

The  granite  does  not  represent  a continuous  phase 
of  development.  Over  considerable  areas  the  coarser 
granite,  which  among  the  prospectors  and  miners  is 
known  as  “bull  rock,”  appears  to  have  no  regularity  of 
arrangement.  More  frequently  the  coarser  portions 
run  through  the  medium  g'rained  granite  in  the  form  of 
irregular  streaks  without  any  well  marked  line  of  sep- 

* Geology  of  the  Black  Hills  of  Dakota,  p.  70. 

t Newton,  Henry.  Geology  of  the  Black  Hills  of  Dakota,  1880. 

Carpenter,  Franklin  R.  Notes  on  the  Geology  of  the  Black  Hills.  Pre- 
liminary Report  of  the  Dakota  School  of  Mines,  1888. 

Crosby,  W.  O.  Geology  of  the  Black  Hills  of  Dakota,  1888. 

Van  Hise,  C.  R.  The  Pre-Cambrian  Rock  of  the  Black  Hills,  1890. 


2 


18  BULLETIN  OF  THE  SOUTH  DAKOTA  SCHOOL  OF  MINES. 


aration.  In  many  places,  however,  the  coarser  mater- 
ial, which  is  pegrnatitic  in  character  and  frequently 
partakes  of  the  nature  of  graphic  granite,  is  observed 
in  distinct  dikes,  they  being-  oftentimes  found  cutting- 
throug-h  the  body  of  medium  grained  granite  as  clearly 
and  sharply  defined  as  if  outlined  with  a pencil.  This 
feature  is  confined  to  no  particular  portion  of  the  area 
studied,  but  it  was  found  perhaps  best  developed  south 
of  Middle  Squaw  creek,  about  two  miles  north-north- 
west of  Sheep  mountain.  Apparently  many  of  the 
dikes,  the  outlines  of  which  are  irreg-ular  or  obscure, 
are  really  formed  in  the  same  way  as  the  more  clearly 
defined  dikes  but  unequal  weathering-  of  the  general 
rock  surface  has  in  the  case  of  the  former  obliterated 
that  which  would  be  clearly  shown  in  a smooth  cross 
section. 

In  many  of  the  better  defined  dikes  the  texture  at 
the  edg*e  is  finer  than  toward  the  center,  and  not  in- 
frequently the  crystals  are  arranged  uniformly  per- 
pendicular to  the  wall  of  the  dike.  This  feature  is 
particularly  prominent  in  the  case  of  tourmaline  when 
abundant  crystals  of  this  mineral  occur  in  the  nar- 
rower dikes.  It  is  well  known  that  the  main. masses  of 
granite,’  which  are  generally  lenticular  in  shape,  run 
nearly  parallel  with  the  strike  of  the  schists  and  quart- 
zites as  first  pointed  out  by  Newton. * The  smaller 
dikes  cut  these  in  various  directions. 

Owing-  to  the  possible  influence  which  they  may  have 
upon  the  economic  development  of  the  area,  considera- 
ble attention  was  gdven  to  the  study  of  the  direction  in 
which  the  dikes  run.  The  results  show  that  a larg*e 
proportion  of  them  extend  radially  toward  Harney 
peak,  but  there  seems  so  many  exceptions  that  the  ob- 
servations are  probably  of  little  value. 

Ordinarily  the  dikes  wherever  well  exposed,  whether 
in  g'ranite  or  in  quartzite,  weather  more  rapidly  than 
the  main  mass  of  rock  so  that  the  position  and  direc- 
tion of  the  dikes  may  be  readily  traced.  This  is  par- 


* Geology  of  the  Black  Hills  of  Dakota,  p.  73. 


BULLETIN  OF  THE  SOUTH  DAKOTA  SCHOOL  OF  MINES.  19 


ticularly  true  when  the  dikes  cut  through  fine  grained 
granite  or  quartzite.  Here  the  coarse  crystals  easily 
disintegrate  and  shrubs  and  small  trees  quickly  spring 
up  to  mark  the  line  of  rapid  weathering.  On  the  other 
hand,  the  dikes,  when  cutting  through  schistose  rocks, 
are  found  generally  to  be  less  easily  disintegrated  than 
the  schist,  and  therefore  project  above  the  general  sur- 
face. 

Metamorphic  Rocks. — T hese  include  the  schists  and 
quartzites  which  are  found  intimately  associated  in 
varying  quantity  throughout  the  region  studied,  but 
which  predominate  only  in  the  southern  and  eastern 
portions.  rfihev  do  not  make  up  the  entire  rock  mass 
over  any  extensive  well  defined  area,  granite  being 
always  present  in  greater  or  less  amount  in  the  form 
pf  dikes  or  irregular  masses. 

In  the  accompanying  geological  map  an  attempt  has 
been  made  to  indicate  the  relative  proportions  of  the 
metamorphic  rocks  and  the  granite.  The  larger  and 
more  important  areas  are  located  and  defined  with 
some  degree  of  accuracy  but  no  effort  has  been  made 
to  reproduce  in  detail  the  intricate  relations  of  the 
various  rock-masses  throughout  the  entire  area.  This 
was  wholly  incompatible  with  the  time  at  our  disposal, 
and,  c wing  to  the  many  difficulties  to  be  encountered, 
could  at  best  lead  only  to  questionable  results.  For 
the  distribution  of  the  rocks  in  the  immediate  vicinity 
of  our  camp  the  reader  is  referred  to  the  accompany- 
ing paper  by  Professor  Forsyth. 

/in  places,  the  original  bedding  of  the  metamorphic 
rocks  is  still  discernible.  An  example  of  this  may  he 
seen  at  the  roadside  one-half  mile  west  of  Otis.  A 
photograph  of  this  out-crop,  through  which  runs  a dike 
of  pegmatite  is  shown  in  figure  7.  Areas  in  which 
quartzites  abound  are  usually  indicated  by  ridges. 
This  feature  is  particularly  prominent  in  the  case  of 
Spokane  ridge,  Saddleback  ridge,  and  Sheep  mountain, 
and  is  quite  noticeable,  although  less  pronounced,  in 
many  of  the  lower  ridges  and  hills  to  the  east.  Localities 
occupied  chiefly  by  schists  are  represented  by  valleys. 


20  BULLETIN  OF  THE  SOUTH  DAKOTA  SCHOOL  OF  MINES. 


Owing-,  however,  to  the  fact  that  the  granite  is  also  in- 
clined to  weather  more  rapidly  than  the  heavy  quartzite 
the  schistose  valleys  are  not  so  typical  as  are  the 
quartzite  ridg*es. 

The  schistose  rocks  are  made  up  chiefly  of  quartz, 
biotite  and  feldspar,  althoug'h  in  some  restricted  areas 
hornblende  or  g'arnet  is  a prominent  constituent. 
Tourmaline  is  sometimes  present,  althoug-h  never  in 
abundance,  and  graphite  is  occasionally  found.  Musco- 
vite sometimes  takes  the  place  of  the  biotite,  and  not  in- 
frequently these  two  minerals  occur  tog-ether.  Biotite 
is,  however,  much  the  more  common  of  the  two  min- 
erals. The  schists  in  which  hornblende  is  the  chief 
constituent  are  found  in  considerable  abundance  west, 
northwest  and  southwest  of  Otis.  These  appear  to  be 
hig-hlv  metamorphosed  basic  igmeous  rocks,  are  some- 
times g-old-bearing*,*  and  probably  come  within  the 
class  desig-nated  by  Professor  Van  Hise  as  dioritic 
rocks  which  have  partaken  of  the  alteration  effects  of 
the  forces  that  metamorphosed  the  f rag-mental  series.'! 
In  color,  they  are  yery  dark  green,  almost  black,  and 
wherever  seen  are  inclined  to  be  rather  massive. 

In  the  micaceous  schists  the  biotite  is  present  as 
medium  brownish  black  flakes,  pretty  evenly  distrib- 
uted among-  the  quartz  granules.  These  flakes  have  in 
the  main  originated  as  a secondary  product  throug-h  the 
alteration  of  the  original  feldspar.  X The  feld- 
spar is  not  particularly  prominent  in  any  case  but  the 
biotite  and  the  quartz  vary  widely  in  amount  present, 
the  specimens  collected  showing-  almost  all  gradations 
from  a hig-hly  crinkled,  very  dark,  nearly  quartzless 
schist,  to  a massive,  even  grained,  translucent  quartzite. 

The  quartzites  vary  little  in  character,  except  at 
times  thev  show  by  the  presence  and  reg-ular  arrang-e- 
ment  of  mica  or  feldspar  an  approach  to  schistose  con- 
ditions. They  are  usually  compact  and  homog-eneous, 


* Carpenter,  F.  R.  Notes  on  the  Geology  of  the  Black  Hills,  p.  25,  1888. 
t The  Pre-Cambrian  Rock  of  the  Black  Hills,  p.  230,  1890. 
t Ibid,  p.  223. 


C 


BULLETIN  OF  THE  SOUTH  DAKOTA  SCHOOL  OF  MINES, 


21 


Figure  7.  Quartzite  exposure  near  Otis.  Pegmatite  Dike  in  lower  part. 


. BULLETIN  OF  THE  SOUTH  DAKOTA  SCHOOL  OF  MINES.  23 


the  purer  varieties  showing'  quartz^  as  almost  the  only 
constituent.  Clear,  almost  colorless,  varieties  are  not 
uncommon  but  more  often,  owing-  to  impurities,  some 
shade  of  blue,  green  or  red  is  noticeable. 

^Quartz  veins  varying'  in  size  from  a mere  line  up  to 
as  much  as  fifty  feet  or  more  in  thickness  occur  abund- 
antly throughout  the  areas  covered  by  the  schists  and 
quartzites.  Many  of  these  veins  are  g'old-bearing'  and 
it  is  for  this  reason  that  their  study  has  become  of 
importance.  Particular  attention  was  paid  to  the  rela- 
tive agfe  of  these  veins.  They  cut  both  quartzites  and 
schists  in  every  direction,  hence  the  quartz  veins  are 
young'er  than  these  rocks.  So  far  as  could  be  learned, 
the  hornblendic  schists  are  not  excepted,  they  being- 
traversed  by  the  veins  in  all  cases  in  the  same  manner  as 
are  the  micaceous  schists.  The  quartz  veins,  however, 
are  in  turn  cut  by  the  pegrnatite  dikes  so  that  at  ev£ry 
place  where  observation  was  made,  the  veins  proved  to 
be  older  than  the  dikes!  The  importance  wrhich  this 
feature  may  seem  to  have  upon  the  economic  develop- 
ment of  the  g'old-bearing-  veins  is  discussed  by  Pro- 
fessor Forsyth  in  the  accompanying*  paper  of  this 
bulletin.  In  some  places,  quartz  veins  were  found 
traversing-  the  main  body  of  granite  but  these  veins 
were  nowhere  prominent  and  in  g-eneral  they  do  not 
appear  to  be  contemporaneous  with  nor  similar  to  the 
g'old-bearing*  veins. 

The  strike  of  the  schists  and  quartzites  is  consider- 
ably east  of  north.  In  many  exposures  this  is  not 
easily  made  out,  owing-  to  the  disturbing-  influences  of 
the  granite,  but  the  ridg'es  formed  by  the  hard  quartz- 
ite beds  frequently  indicate  the  direction  with  consid- 
erable accuracy.  Spokane  ridg-e  and  Saddleback  ridg*e 
whose  g-eneral  direction  is  about  N 35°  E seem  to  follow 
the  strike  pretty  closely. 

Effort  was  made  to  determine  the  position  and  nature 
of  folds  if  present.  None  of  importance  were  located, 
the  various  disturbances  having*  apparently  obliterated 
the  characteristic  features  of  such  folds  as  may  have 
existed.  Westerly  dips  were  occasionally  found,  but 
in  most  cases  observed  the  dip  is  to  the  east. 


24  BULLETIN  OF  THE  SOUTH  DAKOTA  SCHOOL  OF  MINES. 


♦ 


Joint  planes,  as  might  be  expected,  are  well  devel- 
oped. The  numerous  heavy  quartzite  talus  slopes 
throughout  the  area  are  largely  made  up  of  the  rhom- 
bic blocks  produced  by  these  joint  planes.  In  the 
granite  areas  these  planes,  although  less  abundant, 
have  greatly  aided  weathering  and  it  is  to  this  fact  that 
numerous  rocking  stones  and  many  of  the  picturesque 
needle-like  projections  are  due.  As  previously  sug- 
gested the  pegmatite  dikes  so  common  in  many  parts 
of  the  granite  region  weather  more  readily  than  the 
even  grained  granite  which  the  dikes  traverse  and 
these  may  be  observed  in  some  places  to  have  weath- 
ered out  forming  narrow  crevices  extending  sev- 
eral feet  below  the  general  level  of  the  granite  mass 
thus  simulating  the  effect  of  the  joint  planes.  The 
granite  only  rarely  produces  talus  slopes  of  joint 
blocks  the  fragments  collected  at  the  base  of  the  cliffs 
being  almost  always  fine  and  angular,  forming  a kind  of 
granite  gravel  easilv  removed  by  erosive  agents. 

Irregular  fragments  of  quartzite  and  schist  imbedded 
as  foreign  bodies  in  the  granite  are  of  frequent 
occurrence.  These  masses,  which  in  the  miner’s  lan- 
guage may  be  termed  “horses”  are  of  all  sizes  up  to 
many  feet  or  yards  in  diameter. 

J.JJigure  8 shows  one  of  these  enclosed  bodies 
exposed  at  the  top  of  Saddleback  ridge  about  one  mile 
north  of  Little  Squaw  creek.  The  much  jointed  rock 
is  the  quartzite. 

History. 

The  probable  earlv  geological  history  of  the  South- 
ern Hills  is  briefly  as  follows:  In  Algonkian  time  the 
schists  and  quartzites  were  deposited  as  sediments 
derived  from  land  lying  apparently  either  to  the  west 
or  to  the  northeast  of  the  position  now  occupied  by  the 
Hills.  Later,  these  original  sediments  were  cut  by 
basic  eruptives  at  which  time  more  or  less  metamor- 
phism and  folding*  were  produced.  Subsequent  to  this 
action  the  clastic  rocks  as  well  as  the  basic  eruptives 
were  ramified  by  quartz  veins  many  of  which  are  gold- 


BULLETIN  OF  THE  SOUTH  DAKOTA  SCHOOL  OF  MINES. 


25 


Figure  8.  Quartzite  enclosed  by  granite. 


BULLETIN  OF  THE  SOUTH  DAKOTA  SCHOOL  OF  MIXES. 


27 


bearing-.  Following-*  the  eruption  of  the  basic  rocks 
and  after  most  or  all  of  the  g-old-bearing-  quartz  veins 
were  formed,  extensive  granite  intrusions  occurred. 
Apparently  at  the  time  of  the  intrusion  of  the  basic 
eruptives  the  slaty  cleavag-e  was  produced  and  approxi- 
mately coincident  with  the  granite  intrusions,  the  crys- 
talline schists  and  the  schistose  structure,  so  promi- 
nent in  many  parts  of  the  Hills,  was  developed.’!'  At 
some  time  during-  the  middle  or  latter  part  of  the 
Alg-onkian  period  the  sea  shallowed,  and  the  land  ris- 
ing- above  the  sea  as  an  island,  reached  a considerable 
heig-ht.  The  rocks  thus  broug'ht  under  the  influence 
of  erosive  ag-ents  supplied  the  sediments  which  make 
up  the  Cambrian  rocks  surrounding-  the  Hills. 

Note. 

Throug-h  the  kindness  of  Messrs.  A.  Madill  and 
William  McGarrity,  of  Glendale,  two  members  of  the 
party  were  able  to  visit  the  placer  mines  at  Hayward 
immediately  after  breaking*  camp.  While  there  our 
attention  was  directed  to  a tunnel  which  had  been 
driven  several  years  ag-o  into  a hill  on  the  south  side  of 
Battle  creek,  near  the  placer  working's,  a short  distance 
west  of  town.  The  tunnel,  which  is  known  as  the 
Broken  Hill  mine,  is  almost  immediately  beneath 
the  Cambrian  quartzite,  and  has  penetrated  very 
dark  pyritous  schist  for  a distance  of  perhaps  a hun- 
dred feet.  Near  the  entrance  and  extending*  back  to 
the  end  of  the  tunnel,  melanterite  was  found  in  consid- 
erable abundance,  it  having-  been  formed  in  the  pres- 
ence of  decomposing-  pyrite.  So  far  as  can  be  learned, 
melanterite  has  not  hitherto  been  described  as  being- 
found  in  the  Hills,  and  as  the  beauty,  freshness  and 
quantity  of  the  material  is  rather  out  of  the  ordinary, 
we  deem  it  of  sufficient  importance  to  those  interested 
in  the  mineralog-y  of  the  Black  Hills  to  make  mention  of 
it  here. 

* Todd,  J.  E.  A Preliminary  Report  on  the  Geology  of  South  Dakota, 
p.  134,  Sioux  Falls,  1894. 

I Van  Hise,  C.  R.  The  Pre-Cambian  Rock  of  the  Black  Hills,  p.  241, 
1890. 


28  BULLETIN  OF  THE  SOUTH  DAKOTA  SCHOOL  OF  MINES. 


# 


The  specimens  of  fresh  material  collected  have  a rich 
green  color,  and  partake  more  or  less  of  a fibrous  na- 
ture. The  partially  dehydrated  material  is  g-lossy 
white,  and  shows  a prominent  asbestiform  structure. 
Fresh  specimens  quickly  chang*e  to  this  condition,  un- 
less special  care  be  taken  to  prevent  it.  The  mineral,  in 
a more  decomposed  state  sometimes,  although  rarely, 
shows  a sligffit  yellowish  ting'e,  and  readily  crumbles 
in  the  hand.  Good  crystals  were  not  found. 

The  mineral  occurs  in  string*ers,  sometimes  two 
inches  or  more  in  thickness,  which  ramify  the  pyritous 
schist  in  various  directions.  The  remarkable  feature  in 
connection  with  the  deposit  is,  that  delicately  balanced 
conditions  should  prevail  at  or  near  the  surface  for  a 
considerable  lengfth  of  time  sufficiently  stable  to  allow 
the  formation  of  an  easily  soluble  mineral  in  such  abund- 
ance as  is  the  melanterite  at  this  place. 

The  chemical  composition  of  the  melanterite  is  pecu- 
liar. The  percentage  of  ferrous  sulphate  is  quite  low. 
Potassium  sulphate  is  present  in  considerable  quantity, 
and  free  sulphuric  acid  is  particularly  prominent.  The 
amount  of  water  is  also  very  higffi.  Apparently  the 
excellent  preservation  of  the  material  is  in  considerable 
measure  due  to  the  presence  of  the  free  sulphuric  acid. 
In  the  analysis  which  has  been  made  no  opportunity 
was  given  for  the  careful  selection  of  fresh  material, 
hence  the  exact  results  thus  far  obtained  need  not  be 
given  until  other  analysis  are  made.* 

A minutely  crystalized  brownish  or  wine-colored 
mineral  occurs  in  very  small  quantity  with  the  melan- 
terite. This  mineral  is  also  an  iron  sulphate.  The  gen- 
eral characters  of  the  mineral  indicate  that  it  is  amar- 
antite,  althougfh  positive  evidence  of  this  has  not  yet 
been  definitely  established. 

*The  author  is  indebted  to  Mr.  M.  N.  Bolles  and  Mr.  L.  M.  French,  students 
in  the  School  of  Mines,  for  the  analytical  work. 


HUT 


iLETIN  OF  THE  SOUTH  DAKOTA  SCHOOL  OF  MINES.  29 


MINING  GEOLOGY  AND  MINING. 


BY  A.  FORSYTH. 

I.  Introductory. 

The  object  of  this  survey  was  twofold;  first,  to  study 
geologically  in  the  interest  of  mining  and  of  pure  science, 
a selected  portion  of  the  Black  Hills ; and  second, 
to  give  to  students  of  the  School  of  Mines  practical  geo- 
logical and  topographical  work  in  the  field.  This  two- 
fold object  was,  it  is  thought,  in  considerable  measure 
attained. 

The  work  of  the  students  consisted  mainly  in  making 
a careful  topographical  and  geological  map  of  a gold 
mining  district.  The  work  of  the  instructor  was  that 
of  directing  and  assisting  them,  of  studying  with  them, 
and  of  making  notes  and  observations  on  mineral  depos- 
its at  various  points  outside  the  area  surveyed. 

II.  Chilkoot  Gold  Mining  Region. 

Area  Surveyed. — The  black  square  within  the  cross- 
hatched  area  on  the  map,  Figure  1,  of  the  preceding 
paper,  and  also  the  triangle  marked  “Survey  Camp” 
on  the  map,  Fig'ure  4 of  the  same  paper,  show  the  loca- 
tion of  the  region  surveyed.  It  comprises  about  three- 
quarters  of  a square  mile,  and  covers  the  more  import- 
ant gold  quartz  claims  and  prospect  openings.  On 
page  31  is  the  completed  geological  and  topographical 
map. 

This  selected  area  gains  interest  from  its  newness 
and  from  some  peculiar  features  of  the  occurrence  of 
gold.  There  is  the  interest  of  studying  future  possi- 
bilities, of  balancing  the  indications  for  and  against 
future  successful  development. 

The  surface  features  of  the  country  are  pleasant  and 
promising.  The  map  shows  portions  of  three  hills. 
They  are  of  the  gracefully  rounded  shape  characteris- 
tic of  the  quartzite  ridges  of  the  vicinity.  They  rise 
about  300  feet  from  the  bottoms  of  the  intervening  val- 


30  BULLETIN  OF  THE  SOUTH  DAKOTA  SCHOOL  OF  MINES. 


# 


leys.  The  country  is  clothed  with  the  heavy  pine 
covering*  of  the  Southern  Hills.  Trees  of  two  feet  and 
more  in  diameter  are  abundant.  Pine  is  practically 
the  only  tree  found.  The  spruces  of  the  Custer  region 
are  conspicuously  absent.  The  timber  is  protected  by 
the  laws  g*overning*  the  Forest  Reserve.  Water  is 
found  both  north  and  south  of  the  area  mapped.  On 
the  north  is  Big*  Squaw  creek  ; on  the  south,  Middle 
Squaw  creek.  These  creeks  with  their  tributary 
spring's  carry  the  clear  cold  water  characteristic  of 
the  Alg'onkian  area  of  the  Hills,  j 

Prospecting-. — The  first  quartz  locations  in  this  vicin- 
ity were  made  in  1893.  Previous  to  this  there  had 
been  some  placer  exploration  in  the  bottom  of  the 
gulches.  With  what  success,  it  is  not  known.  The 
claims  located  in  1893,  were  the  Parrish,  the  Chilkoot 
and  the  Detroit,  (map,  p.  33.)  In  prospecting*,  the 
first  ore  soug'ht  was  a quartzite,  distinctive  by  a yellow- 
ish green  cast.  It  was  found  to  contain  small  g*old 
values,  ($1.00  to  $2.00  per  ton).  The  Parrish  was 
located  on  this  material,  but  further  search  for  green 
rock  disclosed  to  the  prospectors  white  quartz  veins 
of  greater  value.  On  such  were  staked  the  Chilkoot 
and  Detroit.  These  veins  rang*e  in  width  from  one 
inch  to  two  feet,  and  are  credited  with  g*old  values  of 
from  $20.00  to  $80.00  per  ton,  with  rich  spots  running- 
much  hig*her.  Much  of  the  g*old  is  free  as  shown  by 
the  pan  tests. 

The  Rocks. — The  rocks  are  members  of  the  Alg*on- 
kian  system  of  the  Hills'".  Quartzite  has  already  been 
mentioned  as  constituting*  the  ore  first  soug'ht.  Be- 
sides this,  there  occur  in  the  area  mapped,  mica  schist, 
granite  with  a pegrnatitic  variation,  and  the  quartz  g*old 
veins. 

In  age,  from  oldest  to  youngest,  the  order  becomes: 

1.  Quartzite. 

(1  a).  Mica  Schist. 

2.  Quartz  veins. 

3.  Granite.  (Pegmatite.) 


* See  Dr.  O’Harra’s  paper,  p.  24. 


BULLETIN  OF  THE  SOUTH  DAKOTA  SCHOOL  OF  MINES.  31 

The  quartzite  is  hard,  close  grained,  white  in  general 
appearance,  but  carrying*  in  small  grains  a fair  per- 
centage of  ferruginous  matter. 

Mica  schist  plays  a very  unimportant  part  in  the 
small  area  under  consideration.  It  occurs  in  several 
opening's  plainly  as  the  result  of  dynamic  metamor- 
phism produced  at  the  time  of  the  shattering*  of  the 
quartzite.  On  this  evidence  it  gains  its  order,  (1  a). 
This  order  is  however  provisional  and  may  apply  only 
to  the  small  occurrence  here  considered.  Two  or  three 
inches  was  the  greatest  thickness  of  schist  observed. 
More  extensive  schistose  masses  occur  not  far  outside 
the  boundaries  of  the  map.  These  however,  cannot  be 
here  discussed. 

The  auriferous  quartz  veins  cut  quartzite  but  not  • 
granite.  Figure  9 gives  an 
example  of  the  relations  of 
quartzite,  auriferous  vein 
quartz,  and  granite.  This 
sketch  is  of  the  Detroit  open- 
ing. It  is  the  type  of  sev- 
eral exposures  in  the  vicinity. 

The  relative  age  of  granite 
and  gold  quartz  here  shown  is 
most  important  to  the  pros- 
pector and  miner.  It  natur- 
ally means  that  they  must  take 
into  consideration  chances  of 
profitable  veins  being  cut  off  by 

. - QUARTZITE,  GOLD  QUARTZ  AND  GRANITF. 

granite  sheets  and  must  calcu- 
late on  the  thickness  and  frequency  of  these  sheets. 

The  gold  quartz  is  clear,  white  and  glassy.  Charac- 
teristic of  it  are  numerous  small  cavities  1-32  of  a inch 
and  less  in  diameter,  containing  little  graphite  crys- 
tals. In  places  there  is  much  iron  stain,  possibly  from 
pyrite  oxidation.  Pyrite  unaltered  does  not  yet  ap- 
pear in  the  present  early  stage  of  development.  The 
gold  occurs  in  very  finely  divided  condition,  usually 
more  abundant  in  the  iron  stained  portion. 

The  g'ranite  is  that  of  the  Harney  Peak  area.  Fre- 


32  BULLETIN  OF  THE  SOUTH  DAKOTA  SCHOOL  OF  MINES. 


# 


quently  it  is  pegrnatitic  in  character.  In  fact  it  is  an 
open  question  if  all  the  granite  in  this  region  had  not 
better  be  called  peg-matiteA 

Attitudes  of  Granite  and  Quartzite. — The  shape  of 
the  granite  masses  and  the  relative  proportions  of 
granite  to  quartzite  present  most  important  problems. 

The  map,  pag*e  33,  gives  proportions  by  area  of  gran- 
ite to  quartzite.  Prom  this  map  also  are  seen  two  ap- 
parent systems  of  quartzite  fissures  now  occupied  by 
the  granite  masses.  There  is  an  east-west  system 
shown  most  plainly  along-  the  southern  end  of  the  De- 
troit claims  and  a north-south  system  branching-  from 
this  and  appearing*  also  in  isolated  granite  patches  on 
other  parts  of  the  map. 

That  all  the  fissures  of  these  systems  are  vertical, 
is  not  assumed.  On  the  contrary  there  is  much  evi- 
dence of  flat  lving*  granite  throug-hout  the  area.  Above 
the  road,  near  the  southwest  corner  of  the  map,  is  a 
cliff  exposure  with  granite  and  quartzite  in  horizontal 
layers.  Near  the  eastern  edg-e  of  the  map  at  the  end 
of  the  Mozambique  claim  are  signs  of  flat  granite. 
Here  appear  some  larg-e  quartzite  horses  flat-lying*,  and 
evidently  but . little  displaced.  Ag-ain  on  the  Chilkoot 
claim,  a tunnel  to  the  vein  is  driven  under  a granite 
roof.  A winze  sunk  a few  feet  below  the  tunnel  level 
cuts  still  another  horizontal  granite  layer.  In  an  open- 
ing- on  the  Parrish,  both  horizontal  and  vertical  granite 
may  be  seen.  Horizontal  sheets  of  an  inch  and  less  in 
thickness  here  are  plainlv  branches  from  a larg-e  verti- 
cal mass.  The  thickness  of  these  horizontal  masses 
where  they  can  be  plainly  observed  is  from  two  feet 
down  to  less  than  one  inch.  It  is  most  probable  that 
in  places  they  are  much  over  two  feet  in  thickness. 

Closely  connected  with  the  attitude  of  the  granite 
masses  is  the  attitude  of  the  enclosing-  (and  sometimes 
enclosed)  quartzite.  Dip  is  hard  to  make  out.  Ther 
layered  structure  of  the  quartzite  is  not  always  appar- 
ent. Where  observed,  however,  in  this  area  the  dips 


*See  Dr.  O’Hara’s  paper,  p.  17. 


BULLETIN  OF  THE  SOUTH  DAKOTA  SCHOOL  OF  MINES.  35 


are  prevailingly  south  and  southeast, — away  from  the 
Harney  Peak  granite  masses.  I have  also  noted  a few 
westerly  dips.*  Such  changing  dip  is  of  course 
expected  in  so  shattered  a region. 

The  position  of  the  quartz  veins  are  highly  inclined. 
Thus  they  appear  in  the  Chilkoot,  in  the  Sunrise  (a 
claim  just  north  of  those  mapped)  and  in  two  of  the 
Detroit  openings.  But  in  another  Detroit  opening 
appears  a flat  lying  mass  of  quartz  about  8 inches  thick. 

Development. — Development  has  nowhere  proceeded 
beyond  40  feet  in  depth.  In  the  Chilkoot  this  maxi- 
mum depth  is  obtained  by  driving  in  a side  hill  a 60 
foot  tunnel  to  meet  the  vein  and  then  sinking  at  the 
end  of  this  tunnel.  The  Detroit  openings  are  not  over 
8 feet  in.  depth.  The  Sunrise,  just  west  of  the  area 
mapped  has  a 20  foot  shaft.  Thus  as  regards  mining 
the  country  is  in  its  infancy. 

Construction  of  the  Map. — To  Mr.  M.  N.  Bolles  and 
to  Mr.  P.  E.  Rockwell,  students  of  the  School  of  Mines, 
belongs  the  credit  of  the  construction  of  the  map.  Of 
the  field  work,  the  topography  was  mostly  done  by  Mr. 
Bolles  and  the  greater  part  of  the  geology  by  Mr. 
Rockwell.  The  map  drawing  is  Mr.  Bolles’  work. 

The  topography  was  sketched  on  a skeleton  of  tran- 
sit and  stadia  lines, — the  fine  broken  lines  of  the  map. 
The  elevations  are  calculated  from  a U.  S.  Geological 
Survey  reference  stake  near  the  southwest  corner  of 
the  map. 

The  geology  was  put  in  first,  on  the  evidence  of  out- 
crops, and  second  on  that  of  the  study  of  the  float. 
The  probable  migration  of  the  float  and  the  relative 
amounts  of  the  two  kinds  of  float,  granite  and  quartzite 
were  both  taken  into  account. 

The  value  of  this  work  to  the  students  engaged  was 
certainly  great.  It  was  the  grasping  and  working  out 
in  the  field  of  a practical  problem. 


*See  Dr.  O’Hara’s  paper,  p.  23. 


36  BULLETIN  OF  THE  SOUTH  DAKOTA  SCHOOL  OF  MINES. 


III.  Notes  on  Mining  Operations  Outside  the 
Area  Surveyed. 

Gold  and  Lead. — It  was  the  writer’s  pleasure  to  see, 
though  not  to  study  an  interesting  gold  property  about 
two  miles  east  of  Custer,  just  off  the  Custer-Hermosa 
road.  This  property  is  known  as  the  Lizzie  Lode.  Its 
special  interest  lies  in  the  character  of  the  ore,  which 
is  blue,  hard  and  siliceous,  much  resembling  the  blue 
siliceous  ore  of  the  Northern  Hills.  If,  as  now  seems 
probable,  it  is  the  blue  refractory  siliceous  ore  of  Bald 
Mountain,  this  occurrence  means  a great  widening  of 
the  siliceous  ore  belt,  coming,  as  it  does  here,  far  south 
on  the  Algonkian  area. 

The  rich  Holy  Terror  and  Keystone  mines  of  Key- 
stone are  perhaps  the  most  interesting,  as  they  are  at 
present  the  most  important  gold  mines  of  the  Southern 
Hills.  They  demand,  however,  more  detailed  notice 
than  can  be  given  here,  and  would  furnish  by  them- 
selves material  for  another  paper. 

Mention  can  merely  be  made  of  the  writer’s  visit  to 
the  mines  and  mills  of  these  properties,  when  by  the 
courtesy  of  Mr.  J.  J.  Payel,  then  superintendent,  an 
underground  trip  was  made  through  the  Holy  Terror. 
It  is  a pleasure  to  see  mines  and  mills  like  these,  well 
equipped  and  managed  in  a thoroughly  businesslike 
way. 

In  the  vicinity  of  Keystone  are  many  other  gold 
properties  in  various  stages  of  development,  but  oppor- 
tunity was  not  offered  to  carefully  study  any  of  them. 
The  Bismarck  should,  however,  be  mentioned  as  at 
present  being  most  actively  developed.  Some  notes 
may  also  be  given  in  regard  to  the  Bullion,  which 
besides  the  Holy  Terror — Keystone  property,  was  the 
only  Keystone  mine  visited. 

Here  is  found  a large  body  of  low  grade  ore  developed 
by  an  open  cut,  and  two  tunnels  with  cross  cuts.  The 
open  cut  is  in  the  hill  crest  and  measures  about  350 
feet  in  length,  50  feet  in  width  and  30  feet  in  depth. 
Below  this  cut,  one  tunnel  300  feet  in  length  is  driven 
into  the  hillside  to  tap  the  ore  body'  at  a depth  of  175 
feet.  200  feet  from  the  mouth  of  this  tunnel  a cross  cut 


BULLETIN  OF  THE  SOUTH  DAKOTA  SCHOOL  OF  MINES.  37 


Figure  io.  Spodumene  crystals,  Etta  Tin  Mine. 


BULLETIN  OP  THE  SOUTH  DAKOTA  SCHOOL  OF  MINES.  30 


of  25  feet  is  made  to  disclose  the  width  of  the  ore  body. 
A second  tunnel  320  feet  in  length  has  been  driven  at  a 
lower  level  in  order  to  tap  the  ore  body  at  a depth  of 
400  feet.  This  tunnel  requires  about  300  feet  more 
drifting*  to  reach  the  ore.  230  feet  from  its  mouth  is  a 
cross  cut  disclosing*  ore. 

At  Spokane  an  interesting*  visit  was  made  to  the  g*a- 
lena  mine  of  the  Crown  Hill  Company.  At  the  time  of 
the  visit,  a hundred  foot  shaft  with  about  eig*hty  feet  of 
drift  to  the  east  and  twenty-five  to  the  west  was  to  be 
seen.  Since  then  the  company  has  sunk  fifty  feet  in 
ore  and  foot  wall.  A body  of  ore  several  feet  in  width 
is  reported  as  disclosed  by  this  sinking*.  At  the  bot- 
tom of  the  shaft  a water  fissure  appeared,  delaying- 
work  until  steam  pumps  could  be  introduced. 

This  ore  is  argentiferous  and  auriferous.  It  is  said 
in  reg*ard  to  its  silver  content,  to  preserve  the  rule  that 
the  silver  runs  half  as  many  ounces  per  ton  as  the  per 
cent  of  lead. 

The  Crown  Hill  Company  is  at  present  making*  an 
experimental  run  of  ore  in  the  concentrating*  plant 
of  the  Glendale  Tin  Co.,  about  two  miles  from  the  Spo- 
kane mine.  The  ore  concentrated,  is  that  of  old  dumps 
made  since  the  beginning*  of  the  development  of  the 
mine.  The  concentration  is  made  by  means  of  a Wil- 
fley  table,  and  is  reported  as  a complete  success.  The 
table  separates  the  minerals  as  desired,  giving*  three 
separate  products,  g*alena,  iron  pyrites  and  tailing’s. 
The  capacity  of  the  mill  with  only  one  table  and  inef- 
ficient rolls,  is  twenty  tons  daily. 

Prom  the  Spokane  mine  twenty-four  carloads  of  hand- 
picked hig*h-g*rade  g*alena  and  one  carload  of  concen- 
trates have  been  shipped. 

Reports  have  recently  been  made  of  a new  g*alena 
vein  at  Hayward.  Much  interest  attaches  itself  to  the 
development  of  the  Spokane  and  other  lead  properties 
of  the  Hills,  since  an  abundant  supply  of  lead  ore  means 
value,  not  only  in  the  lead,  g*old  and  silver  which  it  may 
contain,  but  also  in  its  service  as  a collector  of  the 
precious  metals  in  the  smelting*  of  dry  ores. 

Graphite,  Mica  and  Spodumene. — Graphite  and  mica 


40  BULLETIN  OF  THE  SOUTH  DAKOTA  SCHOOL  OF  MINES. 


have  to  some  extent  been  mined  in  the  vicinity  of  Cus- 
ter. The  graphite  has  been  found  valuable  as  facing* 
for  iron  founder’s  moulds.  The  mica  has  been  used  in 
dynamo  manufacture.  An  occurrence  of  graphite  was 
seen  on  French  Creek  where  the  graphite  appeared  in 
rather  granular  masses  of  varying*  purity  up  to  a foot 
in  thickness  in  close  grained  quartzite. 

A mica  mine  about  two  miles  west  of  Custer  was 
visited.  Here  in  a 30  foot  shallow  cut  in  pegmiatite, 
about  40  mica  books  of  from  8 to  12  inches  in  size 
were  exposed. 

A new  experiment  in  mining*  in  the  Southern  Hills 
has  been  the  recent  breaking*  down  and  shipment  of  a 
carload  of  spodumene  from  the  famous  occurrence  in 
the  Etta  tin  mine. 

Dr.  Carpenter  mentions  these  spodumenes  of  the 
Etta  in  his  “Mineral  Resources  of  the  Black  Hills,” 
pag*e  136  of  the  “Preliminary  Report  of  the  Dakota 
School  of  Mines.”  He  here  describes  their  perfect 
shape  and  wonderful  size,  giving*  one  a leng*th  of  35 
feet.  At  the  time  of  our  visit  none  of  that  leng*th  were 
to  be  observed,  but  the  accompanying*  half  tones,  (Fig*- 
ures  10  and  11)  g*ive  some  idea  of  the  shape,  size  and 
manner  of  occurrence  of  the  crystals  seen  by  us. 
Unfortunately  in  the  production  of  the  copper  plate, 
the  man’s  fig'ure  which  shows  the  scale  in  Fig*ure  10 
failed  to  come  out  clearly.  A careful  inspection  will 
however  disclose  it. 

This  experimental  carload  of  spodumene  was  mined 
for  Reinbold  & Co.  of  Omaha  by  Mr.  M.  Dodg*e  of 
Rapid  City.  Thirty  tons  were  taken  out.  The  mining* 
of  this  material  spoiled  of  course  all  those  larg*e  crys- 
tals previously  exposed.  Fortunately  our  photographs 
were  taken  before  the  mining*  operations  commenced. 

The  expenses  of  mining*  on  this  experimental  lot 
were  $6.00  per  ton.  The  spodumene  proved  about  one- 
fifteenth  of  the  material  mined.  The  writer  has  as  yet 
been  unable  to  obtain  information  in  reg*ard  to  the 
chemical  analysis  of  the  material  shipped,  and  the 
exact  use  to  be  made  of  it.  He  is  indebted  to  Mr.  M. 
Dodg*e  for  data  in  reg*ard  to  mining*  and  shipment. 


